Bianchini, D., Castro Alvaredo, O. & Doyon, B. (2015). Entanglement entropy of nonunitary integrable quantum field theory. Nuclear Physics B, 896(July 2), pp. 835880. doi: 10.1016/j.nuclphysb.2015.05.013

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Abstract
In this paper we study the simplest massive 1+1 dimensional integrable quantum field theory which can be described as a perturbation of a nonunitary minimal conformal field theory: the Lee–Yang model. We are particularly interested in the features of the bipartite entanglement entropy for this model and on building blocks thereof, namely twist field form factors. Nonunitarity selects out a new type of twist field as the operator whose twopoint function (appropriately normalized) yields the entanglement entropy. We compute this twopoint function both from a form factor expansion and by means of perturbed conformal field theory. We find good agreement with CFT predictions put forward in a recent work involving the present authors. In particular, our results are consistent with a scaling of the entanglement entropy given by ceff/3 logℓ where ceff is the effective central charge of the theory (a positive number related to the central charge) and ℓ is the size of the region. Furthermore the form factor expansion of twist fields allows us to explore the large region limit of the entanglement entropy and find the nexttoleading order correction to saturation. We find that this correction is very different from its counterpart in unitary models. Whereas in the latter case, it had a form depending only on few parameters of the model (the particle spectrum), it appears to be much more modeldependent for nonunitary models.
Item Type:  Article 

Subjects:  Q Science > QA Mathematics Q Science > QC Physics 
Divisions:  School of Engineering & Mathematical Sciences > Department of Mathematical Science 
URI:  http://openaccess.city.ac.uk/id/eprint/12202 
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